Scientists in Italy compared the progress of asthma patients who were randomly assigned specific lifestyle-changing regimes or continued living as normal for a period of eight weeks.

At the end of the study those who took exercise classes three times a week and ate a healthy low-glycaemic index (GI) diet rich in protein, fruit and vegetables rated their asthma symptoms score 50 per cent lower than patients in the non-intervention control group.

Participants who only altered their exercise level or diet, but not both, reported a 30 per cent improvement in symptoms.

Dr Louise Toennesen, from Bispebjerg University Hospital in Copenhagen, Denmark, said: "People with asthma sometimes find exercise challenging and this can lead to an overall deterioration in their fitness.

"Our study suggests that non-obese asthma patients can safely take part in well-planned, high-intensity exercise.

"It also shows that exercise combined with a healthy diet can help patients control their asthma symptoms and enjoy a better quality of life.

"These are important findings since we know that not all patients have good control over their symptoms and consequently can have a lower quality of life.

"We also know that many patients are interested in whether they can improve their asthma control with exercise and a healthy diet.

"Our research suggests that people with asthma should be encouraged to eat a healthy diet and to take part in physical activity."

A low GI diet is one that releases sugar slowly into the blood and helps maintain a well-balanced metabolism.

Results from the study, which involved a total of 125 participants, were presented at the European Respiratory Society International Congress in Milan, Italy.

The research did not show a clear improvement in lung function, but found that the diet and exercise combination improved symptom control and quality of life.